The cardiac muscle.

The heart is the pump that keeps blood circulating throughout the body and thereby transports nutrients, breakdown products, antibodies, hormones, and gases to and from the tissues. The heart consists mostly of muscle, the myocardial cells (collectively termed the myocardium), arranged in ways that set it apart from other types of muscle. The outstanding characteristics of the action of the heart are its contractility, which is the basis for its pumping action, and the rhythmicity of the contraction.

Circulation of blood.

The cardiovascular, or circulatory, system in humans is composed of the heart and the blood vessels—arteries, veins, and capillaries. Its purpose is to provide nutrients and oxygen to the tissues and to remove wastes from them. It is also where the body fights infections.
The human heart is a pear-shaped muscular organ about the size of a fist. A wall of muscle, the septum, divides the right side from the left. Each of these two sides is further divided into an atrium, or upper chamber, and a ventricle, or lower chamber. The human heart beats 60 to 80 times a minute while a person is at rest. The heart rests only about 0.4 second between beats.

Circuits of the circulatory system.

Circulation of blood consists of two main circuits. Pulmonary circulation carries blood from the heart to the lungs where waste gases, mostly carbon dioxide, are removed from the blood, and oxygen is taken on by hemoglobin in the erythrocytes, or red blood cells (see Blood). The blood then returns to the heart and is pumped to other parts of the body in the systemic circulation, which comprises the blood supply to the entire body except the lungs. Within the systemic circulation is the portal circulation, which supplies blood to the liver. Capillaries and veins carrying nutrient-rich blood from the digestive organs merge to form the portal vein, leading to the liver. Blood from the liver reenters the systemic circulation via the inferior vena cava.

Electrical conduction system of the heart.

The normal electrical conduction in the heart allows the impulse that is generated by the sinoatrial node (SA node) of the heart to be propagated to (and stimulate) the myocardium (muscle of the heart). When the myocardium is stimulated, it contracts. It is the ordered stimulation of the myocardium that allows efficient contraction of the heart, thereby allowing blood to be pumped round the body. Under normal conditions, electrical activity is spontaneously generated by the SA node. This electrical impulse is propagated throughout the right and left atria, stimulating the myocardium of the atria to contract. The conduction of the electrical impulse throughout the atria is seen on the ECG as the P wave.

Coronary heart disease

Coronary heart disease is the progressive reduction of blood supply to the heart muscle due to narrowing or blocking of the coronary arteries. Reduction in blood supply causes oxygen deprivation to the cells.

Depending upon its duration, the consequences of oxygen deprivation vary. Short-term oxygen deprivation can cause Angina Pectoris. Long-term, severe oxygen depletion causes Heart Attack. Coronary bypass or Angioplasty is needed if medication and diet do not control coronary heart disease. 

General structure and function of heart

The heart is the center or seat of power of the circulatory system. A person's heart is roughly of the same size as his/her closed fist. This should give you an approximate estimate of the size of your heart. Here are some statistics about the human heart:

• Rate of pumping: 4 quarts or 3.8 liters per minute.
• Weight: about 8 to 12 ounces or 230 to 340 grams.
• Number of beats per minute: 72 times per minute.

Taking into consideration the fact that a person's average lifetime is 70 years, it will beat about 2 1/2 billion times and pump a total of 35 million gallons (132 million liters) or more of blood from birth to death! Quite a huge figure!